Update badges, remove fuzzit leftovers. (#4886)

Makefile.fuzz

-# Makefile for fuzzing
-#
-# With https://app.fuzzit.dev/ we are continuously fuzzing CoreDNS.
-#
-# Use go-fuzz and needs the tools installed. For each fuzz.go in a plugin's directory
-# you can start the fuzzing with: make -f Makefile.fuzz <plugin>
-# e.g.
-#
-# 	make -f Makefile.fuzz forward
-#
-# Each plugin that wants to join the fuzzing fray only needs to add a fuzz.go that calls
-# the plugin's ServeDNS and used the plugin/pkg/fuzz for the Do function.
-#
-# Installing go-fuzz is very tricky because it does not support Go modules, see the `Makefile`
-# for the current trickery. The following may do the trick:
-#
-# GO111MODULE=off go get github.com/dvyukov/go-fuzz/go-fuzz-build
-
-REPO:="github.com/coredns/coredns"
-FUZZIT:=v2.4.35
-# set LIBFUZZER=YES to build libfuzzer compatible targets
-
-FUZZ:=$(dir $(wildcard plugin/*/fuzz.go)) # plugin/cache/
-PLUGINS:=$(foreach f,$(FUZZ),$(subst plugin, ,$(f:/=))) # > /cache
-PLUGINS:=$(foreach f,$(PLUGINS),$(subst /, ,$(f))) # > cache
-
-.PHONY: echo
-echo:
-	@echo $(PLUGINS) corefile
-
-all: $(PLUGINS) corefile
-
-.PHONY: $(PLUGINS)
-$(PLUGINS): echo
-ifeq ($(LIBFUZZER), YES)
-	go-fuzz-build -libfuzzer -o $(@).a ./plugin/$(@)
-	clang -fsanitize=fuzzer $(@).a -o $(@)
-else
-	go-fuzz-build $(REPO)/plugin/$(@)
-	go-fuzz -bin=./$(@)-fuzz.zip -workdir=fuzz/$(@)
-endif
-
-.PHONY: corefile
-corefile:
-ifeq ($(LIBFUZZER), YES)
-	go-fuzz-build -libfuzzer -o $(@).a ./test
-	clang -fsanitize=fuzzer $(@).a -o $(@)
-else
-	go-fuzz-build $(REPO)/test
-	go-fuzz -bin=./test-fuzz.zip -workdir=fuzz/$(@)
-endif
-
-fuzzit:
-	wget --quiet -O fuzzit https://github.com/fuzzitdev/fuzzit/releases/download/$(FUZZIT)/fuzzit_Linux_x86_64 && chmod +x fuzzit
-
-.PHONY: clean
-clean:
-	rm *-fuzz.zip

README.md

 [![CoreDNS](https://coredns.io/images/CoreDNS_Colour_Horizontal.png)](https://coredns.io)
 
 [![Documentation](https://img.shields.io/badge/godoc-reference-blue.svg)](https://godoc.org/github.com/coredns/coredns)
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-[![fuzzit](https://app.fuzzit.dev/badge?org_id=coredns&branch=master)](https://fuzzit.dev)
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